How long can a sub cable be?

I've seen them being sold in 12 and 18 foot lengths. What if I need it 30 fett long?
Thanks
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Jake T
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When you first get a external sub, people often buy 25' of CATV coax from Radio Shack, and add some "F-to-RCA" adaptors and create a very long cable for about $12. This allows them to put the sub in nearly any corner of the room while playing with positions.
If you decide to run coax in the walls (needing 30+ feet), the CATV coax also works fine.
Cables tend to be rated by their upper-limit of frequency. The frequencies below 120 hz tend to be trivial compared to the RF or Mhz frequencies that most of these cables were designed to carry.
Even if you bought a nice BetterCables sub-woofer cable to your custom length, the coax used would be RG6, which has the same size conductor/shielding as the CATV RG6.
Hope this helps.

I did almost exactly what Bob said. the shack had a 24' RCA-looking cable that had the right specs. i bought 2: one for the SVS and one for the CD player's coax-out. both work fine.
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Actually the audio spectrum is usually transmitted over 50 ohm cable. Coax is 75 ohm, and not optimized for audio applications. It's optimized for video. 50-52 ohm cable is characteristically stranded wire, of a heavier guage than standard RG-6 coax.
In fact for longer applications, I would as good as recommend the audio cable over the coax for best results. YMMV.
CAT almost did sub cables with coax, but in the end, the proper cable for the job was shielded 3 wire audio cable.
Lex
CATCables
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Some assert that a cable's characteristic impedance is of little or no importance at audio frequencies. The reasoning is that, at audio frequencies, transmission line effects are not significant. Therefore, only the cable's lumped LCR parameters matter. Remember: a cable's characteristic impedance is not its DC resistance!
So, it is very much possible for a 75 ohm video cable to function very well as an audio interconnect. The Belden 89259 , which is a 75 ohm cable, is very highly regarded over on Audio Asylum .
To answer the original question, 30 feet should be no problem.
Using multiple adapters does increase insertion loss. You're better off cutting off the original connectors and attaching the desired connectors.

What exactly is a F-to RCA adapter? I assume the F is the standard end of a coax cable (the part that you plug and screw into the back of the cable box)? Then you screw into that piece a standard RCA plug? Is that right? I am wondering since I need a much longer sub cable as well.
THanks,
Allan

What if I need it 30 fett long?
If you are using a good shielded cable such as RG6 coax, the length of the cable is not an issue until it becomes VERY long. 30 feet is definitely no problem.I hear there is substantial signal loss when using adapters... wouldn't you be better off just using regular RCA cable?

1) The signal loss from using adapters is insignificant - especially if you only have one at each end.
2) There is no such thing as "RCA cable." RCA is a type of connector.Actually the audio spectrum is usually transmitted over 50 ohm cable. Coax is 75 ohm, and not optimized for audio applications.
Lex, technically what you've said is correct. Practically speaking, however, it is misleading. Many high-end audio cables are made using 75-ohm coax for three reasons. First, RG6 coax is highly resistant to interference. Second, the actual impedance of most non-coax audio cables typically ranges from 25-200 ohms. As a result, the 75 ohm coax with true 75-ohm connectors is in fact closer to the 50 ohm standard. And third, as Steven has correctly noted, at audio frequencies, the cable's characteristic impedence is of little or no importance.
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